1. Field of the Invention
The present invention generally relates to a semiconductor device and, more specifically, to a semiconductor device having a registration measurement mark used in a step of lithography.
2. Description of the Background Art
The registration measurement mark is used for measuring registration accuracy between two steps of lithography. A conventional method of manufacturing a semiconductor device including the steps of lithography will be described.
Referring to FIG. 13, a semiconductor substrate 1 is divided into a scribe line region and a circuit region.
Referring to FIG. 14, on semiconductor substrate 1, a first electrode layer 2 which will be an electrode, is formed. On the first electrode layer 2, a resist pattern 3 having an electrode pattern is formed.
Referring to FIGS. 14 and 15, using resist pattern as a mask, electrode layer 2 is etched to form electrodes 4a and 4b. Referring to FIG. 16, an interlayer insulating film 5 of SiO.sub.2 is formed on semiconductor substrate 1 to cover electrodes 4a and 4b. On interlayer insulating film 5, a resist pattern 6 having openings above electrodes 4a and 4b is formed.
Referring to FIGS. 16 and 17, using resist pattern 6 as a mask, interlayer insulating film 5 is etched to form contact holes 5a and 5b in interlayer insulating film 5.
Referring to FIG. 18, a second electrode layer 7 is formed on semiconductor substrate 1 to be connected to electrodes 4a and 4b through contact holes 5a and 5b. Referring to FIGS. 18 and 19, second electrode layer 7 is patterned, and a resist pattern 8 having patterns above a portion where a registration measurement mark 9 is to be formed and above portions where main patterns 10a and 10b which are intended for the essential circuitry, hereinafter referred to as intended patterns are to be formed, for the subsequent forming of registration measurement mark 9 and intended patterns 10a and 10b.
Thereafter, using resist pattern 8 as a mask, the second electrode layer 7 is etched, and in this manner, registration measurement mark 9 and intended patterns 10a and 10b are formed.
Referring to FIG. 20, a second interlayer insulating film 11 is formed on semiconductor substrate 1 to cover registration measurement mark 9 and intended patterns 10a and 10b. Thereafter, on the second interlayer insulating film 11, a resist pattern 12 having an opening 12c above registration measurement mark 9 and openings 12a and 12b above intended patterns 10a and lob is formed on the second interlayer insulating film 11.
At this time, positional deviations or offsets between opening 12a and intended pattern 10a and between opening 12b and intended pattern 10b are too small to be detected. Therefore, positional deviation between opening 12c and registration measurement mark 9 having larger area than intended patterns 10a and 10b is detected. The positional deviation is detected optically, that is, using a light beam, which light beam pierces through interlayer insulating film 11. When it is confirmed that the positional deviation between registration measurement mark 9 and opening 12c is within a tolerable range, it is also confirmed that positional deviation between intended pattern 10a and opening 12a is within the tolerable range, and that positional deviation between intended pattern 10b and opening 12b is also within the tolerable range.
If positional deviation between registration measurement mark 9 and opening 12c is out of the tolerable range, resist pattern 12 is removed, a new resist pattern 12 is again formed on the second interlayer insulating film 11, and by patterning the newly provided resist pattern, openings 12a, 12b and 12c are formed again. By repeating such an operation, it is ensured that positional deviation between registration measurement mark 9 and opening 12c is within the tolerable range, and thereafter, the process proceeds to the next step.
Referring to FIG. 21, using resist pattern 12 as a mask, interlayer insulating film 11 is etched to form contact holes 11a, 11b and 11c. Though not shown, a third electrode layer connected to intended patterns 10a and 10b through contact holes 11a and 11b is formed. By repeating these steps, a semiconductor device having multi-layered interconnection structure is formed. Semiconductor substrate 1 is diced along the scribe line region, and chips are formed.
The conventional semiconductor device has been manufactured through the above described method.
Referring to FIG. 20 and corresponding plan view of FIG. 22, intended patterns 10a and 10b are formed in the circuit region, while registration measurement mark 9 is formed in the scribe line region.
Referring to these Figures, accordingly, there is a level difference or step between the surface of registration measurement mark 9 and the surface of intended patterns 10a and 10b. The amount of deviation between registration measurement marks 9 and opening 12c of resist 12 is detected along X and Y directions. Here, as there is a step or level difference between registration measurement marks 9 and intended patterns 10a and 10b, even if the amount of deviation between registration measurement marks 9 and opening 12c of resist pattern 12 is within the tolerable range, this is not accurately reflected on monitoring of the intended patterns, and as a result, intended patterns 10a and 10b are sometimes undesirably deviated from openings 12a and 12b of resist pattern 12. Such deviation hinders successful connection between intended pattern 10a and an electrode formed thereon.
Such a deviation is generated because of the fact that registration measurement mark 9 and intended patterns 10a and 10b have different points of focus at the time of exposure, as there is a level difference. More specifically, such a deviation is caused by an aberration resulting from different points of focus.
FIG. 23 shows a relation between amount of deviation caused by aberration and depth of focus. Referring to FIG. 23, assuming that there is a level difference of 0.6 .mu.m between the intended pattern in the circuit region and the registration measurement mark in the scribe line region, there is a difference of 0.06 .mu.m in the depth of focus. In that case, it can be seen from the figure that the positional deviation caused by aberration would be 10 to 15 nm. This is the reason why the intended pattern cannot be accurately monitored utilizing the registration measurement mark.